Estrogen receptor modulators are a class of compounds that act on the estrogen receptor. These compounds can be pure agonists (mimicking estrogen), pure antagonists, or mixed agonist-antagonists (sometimes referred to as Selective Estrogen Receptor Modulators (SERMs)). For example, estradiol (A) is a pure agonist, fulvestrant (B) is a complete antagonist, and tamoxifen (C) and raloxifene (D) are SERMs.
Most breast cancers express estrogen receptors (ER), and their growth is driven by the action of estrogen at its receptors, primarily at ER alpha. This type of cancer is treated with an estrogen antagonist, which competes with estrogen for binding to the receptor, but does not activate it, preventing estrogen driven growth. Partial anti-estrogens like raloxifene and tamoxifen retain some estrogen-like effects, including an estrogen-like stimulation of uterine growth, and also, in some cases, an estrogen-like action during breast cancer progression which actually stimulates tumor growth. In contrast, fulvestrant, a complete anti-estrogen, is free of estrogen-like action on the uterus and is effective in tamoxifen-resistant tumors. A recent study also suggests that fulvestrant is substantially superior to the aromatase inhibitor anastrozole in treating metastatic breast cancer (Robertson et al. J Clin Oncol (2009) 27(27):4530-5).
Estradiol is a naturally-occurring female estrogenic hormone. Raloxifene was disclosed by Eli Lilly in 1981 (U.S. Pat. Nos. 4,418,068; 5,478,847; 5,393,763; and 5,457,117) for prevention of breast cancer and treatment of osteoporosis. Fulvestrant was disclosed by Imperial Chemical Industries (ICI) in 1983 (U.S. Pat. No. 4,659,516, expired in 2007 with a patent term extension; U.S. Pat. Nos. 6,774,122 and 7,456,160). Tamoxifen was also disclosed by ICI in the '516 patent. Tamoxifen was developed for the treatment of breast cancer on the basis of strong antagonism of estrogen action in mammary tissue (Jordan, J. Cell. Biochem. 51 (1995)).

The degree of anti-estrogenicity is often assayed by exposing female, immature (preferably ovariectomized) rodents to test doses of the compound both in the absence (agonist mode) and presence (antagonist mode) of estrogen. Tamoxifen and other partial anti-estrogens stimulate uterine weight gain in the agonist mode and only partly block estrogen-driven uterine weight gain in the antagonist mode. Fulvestrant and other complete anti-estrogens do not stimulate uterine weight gain in the agonist mode and completely block estrogen-driven weight gain in the antagonist mode. The induction of estrogen-regulated alkaline phosphatase expression in human uterine cancer cell growth in culture can be used to distinguish partial and complete anti-estrogenicity and correlates well with the rodent weight gain assay.
Tamoxifen and fulvestrant both inhibit cultured human breast cancer cell proliferation provoked by estrogen. However, fulvestrant more fully inhibits the proliferation when provoked with growth factors, especially of the insulin/insulin-like growth factor family. Thus the inhibition of growth-factor driven breast cancer cell proliferation and the effect on uterine weight provide two assays which can distinguish between complete and partial anti-estrogens.
Tamoxifen binding stabilizes the estrogen receptor whereas fulvestrant and chemically related antiestrogens, such as ICI-164384 and RU-58668, cause degradation of the estrogen receptor. (Dodge et al, J. Bone Miner. Res., 8 (Suppl 1, S278 (1993); Wakeling, Breast Cancer Res. Treat. 25, 1 (1993); Baer et al, Calcified Tissue Int., 55, 338 (1994). However, some compounds, like GW-5638 (Wu et al, Mol. Cell., 18, 413 (2005), and OP1075, described below, degrade the receptor but are partial estrogens—that is, not complete anti-estrogens. Thus the ability to degrade the estrogen receptor does not ensure complete antiestrogenicity. The ability to induce degradation of the receptor is nonetheless a factor that differentiates the behavior of tamoxifen and fulvestrant and may be desirable in a drug to treat breast cancer.
Fulvestrant, which degrades the estrogen receptor, incorporates a core of 17-beta estradiol. It has a long flexible aliphatic side chain that blocks oral absorption. The estradiol core blocks oral absorption and the long flexible aliphatic side chain makes the drug very insoluble which worsens the problem. Fulvestrant must be injected because of the poor oral bioavailability. Two 5 ml intramuscular depot injections, one into each buttock, must be administered monthly by a health professional. Furthermore, it is unclear whether these two injections provide sufficient drug exposure for optimal action. The drug does not seem to work in pre-menopausal women.
In 1990, an important step in oral anti-estrogen development came with the discovery of a family of high-affinity benzopyran anti-estrogens by Kapil and coworkers. (Sharma et al. (1990) J Med Chem, 33(12):3222-9; Sharma et al. (1990) J Med Chem, 33(12):3216-22). The numbering scheme of benzopyrans is typically:

Sharma et al. showed that the combination of 7-hydroxyl and 4′-hydroxyl groups conferred high-affinity binding of the benzopyran core to the estrogen receptor (Compound G; see Compound 25 of Sharma et al. (1990) J Med Chem, 33(12):3222-9 where R1 and R2 are OH).
Further, Sharma et al. reported that the presence of a methyl group at the 4 position of the benzopyran core enhanced receptor binding affinity, without a hydroxyl group at the 4′-position.
In 1991, Labrie and coworkers filed a patent application which issued as U.S. Pat. No. 5,395,842 (see claim 29) which taught that EM-343 (H), showed superior binding to the estrogen receptor with no loss of anti-estrogen action. EM-343 differed from the Saeed compounds by including the hydroxyl at the 4′-position of a 4-methyl, 7-hydroxyl benzopyran.

In 1995, Labrie et al. filed a continuation-in-part patent application, which issued in 2000 as U.S. Pat. No. 6,060,503, disclosing prodrugs and optically active species of EM-343. Particularly, Labrie et al. disclosed a pure isomer of EM-343, EM-652, referred to as acolbifene (I), which is (S)-3-(4-hydroxyphenyl)-4-methyl-2-(4-(2-(piperidin-1-yl)ethoxy)phenyl)-2H-chromen-7-ol.

Labrie et al. in WO 01/54699 (see FIGS. 4a and 4b) also presented several broad generic Markush formulae of benzopyran-containing compounds, including acolbifene analogs, in which the side chain terminates in various substituted ring systems including pyrrolidinyl, piperidinyl, and methyl-1-pyrrolidinyl and dimethyl-1-pyrrolidinyl.
U.S. Pat. Nos. 7,005,428 and 6,465,445 to Labrie, which claim priority to a June 1998 application describe the following generic formulas for use as anti-estrogenic compounds:
                wherein D is —OCH2CH2N(R3)R4 (R3 and R4 either being independently selected from the group consisting of C1-C4 alkyl, or R3, R4 and the nitrogen atom to which they are bound together being a ring structure selected from the group consisting of pyrrolidino, dimethyl-1-pyrrolidino, methyl-1-purrolidinyl, piperidino, hexamethyleneimino and morpholino); and        wherein R1 and R2 are independently selected from the group consisting of hydrogen, hydroxyl and a moiety converted in vivo in to hydroxyl, and        
                wherein R1 and R2 are independently selected from the group consisting of hydroxyl and a moiety converted in vivo in to hydroxyl;        wherein R3 is a species selected from the group consisting of saturated, unsaturated or substituted pyrrolidinyl, saturated, unsaturated or substituted piperidino, saturated, unsaturated or substituted piperidinyl, saturated, unsaturated or substituted morpholino, nitrogen-containing cyclic moiety, nitrogen-containing polycyclic moiety, and NRaRb (Ra and Rb being independently hydrogen, straight or branched C1-C6 alkyl, straight or branched C2-C6 alkenyl, and straight of branched C2-C6 alkynyl.        
Acolbifene binds to the estrogen receptor alpha with three times the affinity of 17-beta estradiol, the native ligand (Katzenellenbogen (2011) J Med Chem 54(15):5271-82). Since anti-estrogens must compete with estradiol for binding to the estrogen receptor, high affinity binding is an important drug virtue. Both the Labrie '842 and the Labrie '503 patents disclosed benzopyran compounds that can contain an unsubstituted pyrrolidine in the “tail” or R3 position as depicted in Compound F. EM-800, a pivalate prodrug of EM-652, and HCl salts of EM-652 were also described in the '503 patent.
Acolbifene was initially thought to be a complete anti-estrogen. However, careful studies with the rodent uterine assay and human uterine cell alkaline phosphatase assays revealed that it retained some estrogen-like action, about 12% that of estradiol (Labrie et al. “The combination of a novel selective estrogen receptor modulator with an estrogen protects the mammary gland and uterus in a rodent model: the future of postmenopausal women's health?” Endocrinology. 2003 144(11):4700-6). This contrasts with fulvestrant where the residual estrogen-like action is almost unmeasurable. Furthermore, fulvestrant binding induces dramatic degradation of the estrogen receptor, while acolbifene induces either no or modest receptor degradation. Raloxifene and bazedoxifene don't degrade the receptor, but stabilize the receptor to a much lesser degree than tamoxifen.
Acolbifene is orally bioavailable and is currently being positioned for Phase III clinical trials for the treatment of breast cancer by the Canadian company Endoceutics (Founded by Dr. Labrie). A daily oral dose of 40 mg of acolbifene or EM800 in women produces mean drug exposures of 8.3 and 15 ng/ml of circulating acolbifene, respectively. In preclinical studies both forms of the drug are effective against tamoxifen-resistant human breast cancer xenografts growing on immunocompromised mice. In clinical studies the 40 mg dose of EM800 was numerically as effective as anastrozole in preventing progression of metastatic estrogen receptor positive breast cancer.
Starting in 2005, Blizzard and coworkers at Merck published a series of papers on estrogen receptor ligands. They first focused on using a dihydrobenzoxathiin core (J) with alkyl substituted pyrrolidine side chains and linkers as SERAMs (Selective Estrogen Receptor Alpha Modulators) (Blizzard et al. (2005) Bioorg Med Chem. Lett. 15(1):107-13).

The group tried to maximize the estrogen receptor αβ selectivity ratio and minimize uterine activity (e.g., maximize antagonism of uterine activity). They reported that the unbranched linker with 3-methylpyrrolidinyl and 3,4-methylpyrrolidinyl as well as the α-methyl (i.e., a methyl on the α-position of the ethylene) linker with an unsubstituted pyrrolidinyl side chains were noteworthy. Blizzard et al. concluded that minor modifications in the side chain or linker resulted in significant effects on biological activity, especially in uterine tissue.
Blizzard et al. also studied a chromane core (Blizzard et al. (2005) Bioorg Med Chem. Lett. 15(6):1675-81) (Compound K).

The Merck chromane core differs from the acolbifene core by the absence of a double bond in the oxane ring. These structures also had a hydroxyl at position 6 (not 7) of the fused benzene ring. A chromane core with a 2-methylpyrrolidine (but not a 3-methyl) with a methyl on the linker created a nearly complete anti-estrogen, (see compound 12 of the Blizzard et al. paper). Blizzard et al. commented on the differences among anti-estrogenic activities of variously substituted cores, and noted that the size and stereogenic placement of substituents is crucial for receptor potency and selectivity.
In the third publication of this series (Blizzard et al. (2005) Bioorg Med Chem. Lett. 15(17):3912-6); Blizzard et al. again studied the dihydrobenzoxathiin core and reported that their studies have resulted in the discovery that addition of a methyl group to the side chain at the appropriate position and with the right stereochemistry, either on the pyrrolidine ring or on the linker substantially increased estrogen antagonist activity in uterine tissue. Blizzard et al. also reported that the best estrogen antagonist activity in this dihydrobenzoxathiin series was determined to have a methyl group on the pyrrolidine and a methyl group on the linker, with the hydroxyl in the 6-position of the fused benzene ring. Blizzard et al. also noted that to their knowledge, their optimized side chain with two methyl groups represented the first example where a relatively small structural modification of an existing SERM resulted in a conversion of a SERM to a SERAM/SERD (Selective Estrogen Receptor alpha Modulator and Down-regulator).
The Merck team then investigated whether the optimized side chain modification reported for the dihyrobenzoxathiin core was “portable” and could confer strong anti-estrogenicity when appended to different cores (Blizzard et al. (2005) Bioorg Med Chem Lett. 15(23):5214-8). Merck demonstrated that none of the three cores tested (raloxifene, bazedoxifene, or lasofoxifene) became more anti-estrogenic with either the 3-methyl pyrrolidine or the chiral side chain modifications. Blizzard et al. concluded that “The lack of a dramatic effect on the uterine profile upon incorporation of side chains A and B clearly indicates that the side chain Structure Activity Relationship of the dihydrobenzoxathiin SERAMs is not transferable to other platforms.”
In yet another 2005 research publication, Gauthier, Labrie and colleagues reported the synthesis and structure-activity relationships of analogs of acolbifene (Gauthier et al. (2005) J Enzyme Inhib Med Chem, 20(2):165-77). They attempted to improve on the anti-estrogenicity of acolbifene by creating analogs in which the terminal piperidine was either replaced by pyrrolidine or substituted in various ways. All of these analogs proved to be more estrogenic than acolbifene as revealed by the rodent uterus assay. This experience suggests that improvement of the anti-estrogenicity of acolbifene will be a challenge and modifications provide unpredictable results.
Blizzard reviewed the Merck research on anti-estrogens in 2008 (Curr Top Med. Chem. 8(9):792-812). He noted that:                “Selective Estrogen Receptor Modulators (SERMs) have been the subject of extensive medicinal chemistry efforts at several pharmaceutical companies, including Merck . . . . The Merck SERM project involved a large number of talented and dedicated chemists and biologists who worked for several years to discover novel classes of SERMs with a range of selectivities . . . no drugs have yet reached the market as a result of this effort.”        
Indeed, the Merck effort began in the early 1990's and continued well into the 2000's, reflecting impressive science but no commercial products. Their most promising compounds, which included side chains in which the piperidine ring was replaced with a mono- or di-substituted pyrrolidine ring appended to a benzoxathiin core, especially with a 3-R methylpyrrolidine terminus, showed anti-estrogenicity, although not as complete as fulvestrant in the rodent uterus assay. A chiral methyl on atom 2 of the flexible linker also conferred improved anti-estrogenicity. The two features together in a doubly substituted side chain conferred anti-estrogenicity that was similar to fulvestrant. Unfortunately the Merck core had problematic reactive metabolites when investigated in primates, which halted clinical development.
Aragon Pharmaceuticals filed PCT/US2011/039669 (published Dec. 15, 2011 as WO2011/156518), which claimed priority to U.S. Provisional Application 61/353,531 titled “Estrogen Receptor Modulators and Uses Thereof” filed in June 2010. Aragon disclosed large genuses of benzopyran derivatives and at least 71 acolbifene analogs intended for treatment of tamoxifen resistant breast cancer. Aragon appears to have taken the prior art teachings of Merck regarding how to optimize the dihydrobenzoxathiin core, and applied the teachings to the acolbifene benzopyran core. Aragon is considering advancing a drug to the clinic for late stage progressive metastatic disease.
Bazedoxifene is a SERM, under development for prevention and treatment of postmenopausal osteoporosis (Biskobing, D. M. (2007) Clinical interventions in aging 2 (3): 299-303). Lasofoxifene is another SERM under development for the treatment of postmenopausal osteoporosis and vaginal atrophy (Gennari et al. (2006), Expert Opin Investig Drugs 15 (9): 1091-103).
U.S. Pat. No. 5,254,568 discloses benzopyrans as anti-estrogenic agents.
WO2010/145010 discloses a combination of SERM and sex steroid precursor for treating hot flashes and other symptoms.
WO2004/091488 discloses benzopyrans as estrogen receptor modulators.
U.S. Pat. No. 5,840,735 discloses benzopyrans as sex steroid activity inhibitors.
U.S. Pat. No. 6,262,270 discloses a method for the enantiomeric synthesis of acolbifene derivatives.
The object of the present invention is to provide a new improved anti-estrogenic compound for the treatment of medical disorders that are mediated or affected by an estrogen receptor and pharmaceutical compositions and uses thereof.